1. Field of the Invention
The invention relates to a transformer core and, in particular, to a transformer core that can realize a fractional number of turns, and a winding structure utilizing such a transformer core.
2. Description of the Related Art
FIG. 1 shows a conventional transformer core and winding structure, in which the number of turns can only be an integer. In FIG. 1, reference number 10 denotes an E-type core, and reference numbers 11 and 12 denote the primary winding and the secondary winding, respectively.
One problem with the conventional core is that sometimes the number of turns of the transformer is required to be a fractional number, which the conventional core cannot satisfy. For example, when the number of turns of the primary winding is 10 turns, and the transform ratio is required to be 0.33, the number of turns of the secondary winding must be 3.3 turns. Since the number of turns of the secondary winding of a conventional core can only be an integer, there is no choice but to re-design the transform ratio into 0.3 or 0.4, which results in an error of about 9.1% or 21.2%.
Another problem is that in some power switch circuits, the output voltage of the transformer needs to be finely tuned. Since the fractional number of turns cannot be realized in conventional core structures, the output voltage can only be tuned by additional voltage tuning circuits. This results in the increase of both the complexity and the power loss of the power switch circuits.
To overcome the above problems, one conventional solution is to vary the winding of the wires on the core structure. As shown in FIG. 2, the secondary winding 22 has an additional turn on the side post of the core 20. This additional turn on the side post can be treated as an additional 0.5 turn of the secondary winding 22. Using this method, a core structure can realize windings having a turn number of 0.5.
However, this solution still has a limitation in that the number of turns can only be a multiple of 0.5. The number of turns of a core structure still cannot be a fraction other than a multiple of 0.5.